In tooth restoration the bonding strength of restorative dental materials to tooth (enamel and dentin) is of great importance, because insufficient bonding strength cause formation of marginal gaps generating recurrent caries.
When tooth cavities are filled with a polymerizable resin-based tooth filling material, before the filling is introduced, the tooth enamel is treated with an acidic etching solution, for instance a dilute phosphoric acid solution, and is also coated, if necessary, with a sealing material of low viscosity, which typically contains monomeric dimethacrylates and can be hardened chemically or by photopolymerization. Because of their good physical properties sealing materials which in addition to the monomers contain a fine-grained inorganic filler have proven to be particularly suitable. They adhere because they are mechanically anchored in the etched tooth enamel.
From the standpoint of the dental practitioner, however, etching of the tooth dentin is not recommended. Therefore whenever anchoring by etching the tooth enamel is impossible, Such as in cervical cavities, adhesion promotors are used to improve the adhesion between the dentin and the resin. Many such dental adhesion promotors are known, including those described in the following references which are incorporated herein.
Adhesive Restorative Dental Materials 1961, 195-198 contains a report on the adhesion-improving effect of bis-(methacryloyloxyethyl) hydrogen phosphate and of some dihydrogen phosphates containing methacryloyloxy groups.
An adhesive for teeth which comprises a solution of a polymerizable hydrogen phosphate in an organic solvent, such as ethanol, ethyl ether or chloroform, is described in German Examined Patent Application DE-AS 27 11 234 and corresponding U.S. Pat. Nos. 4,259,075, 4,259,117 and 4,368,043.
From European Patent Application 88 527, a material for improving adhesion (called an "adhesion promotor") is known, which comprises a solution of dihydrogen phosphate, having at least three methacryloyloxy groups, in a volatile organic solvent, especially an alkanol. An adhesive or sealing material (called an "intermediate bonding resin") can be used together with this material to increase the adhesion of the tooth filling material to the tooth substance.
From published Japanese Patent Applications 57-56490 and 57-167364, the use of tetramethacryloyloxyethyl pyrophosphate in dental materials is known (Chemical Abstract Vol. 98, 1983, 34, 758 and 204 455).